This document contains 10 multiple choice questions testing knowledge of alkyl halides and their reactions. It addresses topics like bond energies, reactivity of alkyl halides, mechanisms of substitution reactions, products of reactions between alkyl halides and reagents like sodium and hydrogen, and methods for preparing alkyl halides. The explanations provided give insight into factors that determine reactivity and reaction outcomes based on concepts like sterics, stability of carbocations, and properties of leaving groups.

2. • 1. Which C-X bond has the highest bond energy per
mole?
a) C-Br
b) C-Cl
c) C-F
d) C-I
Answer: c) C-F
Explanation: Bond energies depend on many
factors: electron affinities, sizes of atoms involved
in the bond, differences in their electronegativity,
and the overall structure of the molecule. There is
a general trend in that the shorter the bond length,
the higher the bond energy.

3. • 2. Which alkyl halide has the highest reactivity for a
particular alkyl group?
a) R-F
b) R-Cl
c) R-I
d) R-Br
Answer: c) R-I
Explanation: Reactivity order for the alkyl halides
towards Sn2 reaction is R-I>R-Br>R-Cl>R-F. This can
be explained by which halogen atom is a better
leaving group compared to the other.

4. • 3. When ethyl chloride reacts with nascent
hydrogen, what is the formed product?
a) Methane
b) Propane
c) Butane
d) Ethane
• Answer: d) Ethane
Explanation: When an alkyl halide is treated with
zinc and hydrochloric acid, it is reduced to the
respective alkane. The nascent hydrogen formed by
the reaction between zinc and HCl acid reduces
ethyl chloride to ethane.

5. • 4. Which alkyl halide out of the following may
follow both SN1 and SN2 mechanism?
a) CH3-X
b) (CH3)2CH-X
c) (CH3)3C-X
d) (CH3)3C-CH2-X
Answer: b) (CH3)2CH-X
Explanation: (CH3)2CH-X follows both SN1 and SN2
mechanism because the second CH3 of (CH3)2CH-X
further blocks a nucleophile (such as: OH) in
backside SN2 attack, but it increases the stability of
the carbocation resulting from SN1 ionization. As a
result, SN1 and SN2 mechanisms are sometimes
competitive for (CH3)2CH-X.

6. • 5. When two moles of ethyl chloride react with two
moles of sodium in the presence of ether what will
be formed?
a) 2 moles of ethane
b) 1 moles of ethane
c) 2 moles of butane
d) 1 moles of butane
Answer: d) 1 moles of butane
Explanation: Wurtz reaction is method of
preparation of higher alkanes from lower alkyl
halides. This is coupling reaction. In this reaction
alkyl halides are reacted with sodium metal in
presence of dry ether and higher alkanes with even
number of carbon atoms only are formed, by this
method.

7. • 6. Which of the following halide can give best SN2
reaction?
a) Primary alkyl halide
b) Tertiary alkyl halide
c) Secondary alkyl halide
d) All can give SN2 reaction at same rate
Answer: a) Primary alkyl halide
Explanation: A 1° alkyl halide has only one alkyl
group, so it is relatively unstable. It is unlikely to
form a 1° carbocation in an SN1 reaction. Instead, it
will take the lower-energy SN2 path as 1° alkyl is
sterically unhindered. More the steric hinderance
the substrate becomes less susceptible to SN2
attack.

8. • 7. Why alkyl halides are considered to be very reactive
compounds towards nucleophile?
a) they have an electrophilic carbon & a bad leaving group
b) they have a nucleophilic carbon & a good leaving group
c) they have an electrophilic carbon
d) they have an electrophilic carbon & a good leaving group
Answer: d) they have an electrophilic carbon & a good
leaving group
Explanation: Alkyl halides are considered to be very reactive
compounds towards nucleophile because they have an
electrophilic carbon & a good leaving group as we go down
the periodic table, halides that are larger in size will also be
able to distribute their charge over a larger volume, making
them less reactive (less basic). This is why fluoride is a much
poorer leaving group than any of the other halides. So, alkyl
halides are good for nucleophilic substitution reactions.

9. • 8. In primary alkyl halides, carbon attached to the
halogen atom is further attached to how many
carbon atoms?
a) 1
b) 2
c) 3
d) 4
Answer: a) 1
Explanation: As we can see below, carbon attached
to the halogen atom is further attached to one
carbon atom.
Example: CH3-X → Methyl halide
CH3-CH2-X → Ethyl halide
CH3-CH2-CH2-X → n-Propyl halide.

10. • 9. Which of the following is not the method of
preparation of alkyl halide?
a) Darzen’s method
b) Halogenation of alkene
c) Addition of HX on alkenes
d) Hydration of alkene
Answer: d) Hydration of alkene
Explanation: Hydration of alkene is electrophilic
addition of H2O to alkenes which forms alcohol
not alkyl halides.

11. • 10. Which of the following reactant gives the best method of
preparation of alkyl halides when reacts with alcohol?
a) Zn/HCl
b) PCl5
c) SOCl2/ Pyridine
d) PCl3
• Answer: c) SOCl2/ Pyridine
Explanation: The best method of preparation of alkyl halides is a
reaction of alcohol with SOCl2/ Pyridine because by-products formed
in the reaction are SO2 and HCl which are in gaseous form and
escape into the atmosphere leaving behind pure alkyl chlorides.
CH3CH2−OH + SOCl2 → CH3CH2−Cl + SO2↑ + HCl↑